Which is a sign of internal bleeding?

Answer: D — All of the above

Internal bleeding can manifest in various ways, all of which are significant indicators to recognize in a medical emergency. When considering the signs of internal bleeding, bleeding from body cavities serves as a direct indication that blood is escaping from the vascular system within the body, potentially into spaces such as the abdomen or thoracic cavity, which often requires immediate medical attention. Bruising on areas like the neck, chest, abdomen, or sides can also be a telltale sign. Bruising occurs when blood vessels underneath the skin are damaged, allowing blood to leak into surrounding tissues; this can happen even without any external injury, signaling trauma that might involve internal bleeding. Abdominal tenderness accompanied by rigidity reflects a physical response to internal bleeding, whereby the body's muscles contract to guard the area, often in an attempt to brace against pain or protect an injured organ. This rigidity can indicate irritation from blood pooled in the abdominal cavity or pressure exerted by an enlarging hematoma. Since all these signs indicate possible internal bleeding, the answer encompassing all of them is the most accurate representation of the indicators one should watch for in assessing a potential case of internal injury.